You can do that with a boarding pass downloaded from the airline website or emailed to you by the airline. But some airlines like to hide this option in order to force you to download their app.
How can you remotely update a PDF file after someone downloaded it?
Why would you need to do that? The boarding pass has a QR code on it; the QR code links to your ticket. If you need to change your booking, they can email you a new one.
They are referring to gate and time changes
And? These are available on google, on the airline's website, and on screens throughout the terminal. Many airlines will send them to you via SMS. There's no need to have a whole app just to check your gate assignment.
Or I could just use an app and get a push notification.
If you have a half gig spare for such an app these days maybe
I can't remember the last time I received a gate change notification via SMS. App push notifications are more common in my experience.
Some airlines email you a hyperlink that put passes in your Apple wallet from a website. This seems like the ideal case to me.
did you simply ignore what the parent poster wrote about it updating itself with gate numbers etc.?